Launched about two years ago, the site already has more than 10 million monthly visitors and, among social networks, is ranked below only Facebook and Tumblr in terms of average time-spent-per-user per month.

But with massive growth comes major scrutiny.

Choire Sicha at The Awl brought up the question of whether Pinterest might be the most illegal network to hit the Internet yet. More illegal than Napster. More illegal than Megaupload.

Pinterest is a place where users upload photography – sometimes professional, copyrighted photography – that they found elsewhere on the Internet.

We talked to media law attorney Itai Maytal, who's an associate at Miller Korzenik Sommers LLP, to try and understand: Is Pinterest theft on a massive scale? Using what we learned from him, we've created an FAQ to try and answer this question. (Note: this is not an interview with Maytal. Both the questions and answers are ours, unless Maytal is quoted.)

Q: First off, what is Pinterest?

A: Pinterest is a social media site that involves "pinning" pictures you like to 'boards' that you create. Its users are heavily female — maybe as much as 95 percent.

Q: Sounds fun.

A: It is! People love the visual element. Because you can combine pictures from all over the web, as well as your own, and put them in one place, it's sort of like an interactive collage.

Q: But wait: You can use other peoples' photos?

A: Yes.

Q: Isn't that illegal?

A: It's not clear. Pinterest definitely allows users to post other photographers' work to the site. But it's not clear that this is illegal.

In its terms of use, Pinterest actually specifies that users shouldn't pin photos they don't own the rights to, a request that is being ignored to an absurd degree. Even if you link and attribute, that does NOT absolve you of the fact that you took someone else's work and re-appropriated it.

It's all about complying with the DMCA, or the Digital Millennium Copyright Act.

A: On YouTube, you're only allowed to post videos you own the rights to. If a copyright holder sees that you posted one of his or her videos, YouTube will take it down upon complaint.

Q: But is it illegal?

A: Pinterest could be in Fair Use territory (meaning, legally protected). Fair Use law allows people to use work they do not own the copyright to. There are four elements to consider when determining if something is Fair Use:

The purpose and character of the use, including whether such use is of commercial nature or is for nonprofit educational purposes

The nature of the copyrighted work [is it fictional or factual]

The amount and substantiality of the portion [of the work] used in relation to the copyrighted work as a whole

The effect of the use upon the potential market for, or value of, the copyrighted work

The big one is that first question. If the use is transformative — if something new is being created by using the picture — then it can be construed as Fair Use.

One of the most famous cases of this, and one that Maytal pointed to as likely to be a major precedent, is Perfect 10 v. Google. A nude-image subscription service. Perfect 10 sued Google because Google's Image search showed pictures that Perfect 10 hid behind a paywall. It claimed that Google was doing it irreparable harm by showing the pictures in its search.

Google won the case. The courts ruled that Google Image search is Fair Use because it's transformative.

Maytal told us, "The use of the thumbnails was highly transformative, allowed users to get to a source of information that they couldn’t otherwise get." Google Image search becomes a social benefit and a reference tool.

Q: So how does Pinterest stack up in these Fair Use conditions?

A: Not well. On question 2, photography is inherently creative — photos are not facts — so that's a point against Pinterest. On question 3, Pinterest, in many cases, allows users to see photos from other sources in their full, original form on Pinterest's site. That's the work in its entirety.

On question 4, if users are able to see the work in its entirety, then they have no need to click through to see it at its source, potentially affecting the market. Also, even if you argue that Pinterest helps photographers or businesses sell products, that doesn't necessarily help.

Q: Isn't helping someone sell their stuff always good?

A: No. A case involving J.D. Salinger's attempt to stop his letters from being published established that a copyright holder always has the right to control the use of his work, even if that means he'll make less money.

Q: What about that first question, of whether Pinterest is transformative?

A: This will be the big issue, and what will likely determine Pinterest's legality. The fact that Pinterest isn't making any money yet definitely helps. Once it starts monetizing these pictures, it will become harder to argue that it's Fair Use.

Money isn't the biggest issue, though. The biggest issue is whether the use is a public service, or creates something new. Pinterest could potentially argue that it's a search or reference tool. But Google only provides thumbnails, which is transformative; you have to go to the original source to see the full picture. That's not the case with Pinterest, and that could be the killer.

Q: Couldn't Pinterest just take down the pictures that are infringement?

A: Yes, and they're supposed to. But they're not doing that. And the question of whether it's up to the service or the users to guard copyright is still being hashed out in the courts.

Q: How is this any different than Tumblr? I post stuff that isn't mine there all the time.

A: Good question! It's not really different. This could be an issue for Tumblr soon enough as well. The difference is that Pinterest seems designed almost entirely for the theft of others' copyrighted material, whereas Tumblr's a blogging service like any other on the Internet, just easier to use.

Q: So, is Pinterest illegal?

A: Quite possibly. Until there's a legal challenge against the site, it'll be hard to know. Pinterest could have some legitimate arguments in favor of itself: Claiming it's a search tool, saying it drives traffic elsewhere, arguing that the way it shows pictures is transformative.

But the big problem is that it grabs entire copyrighted works to re-post. This could be hard to overcome, especially as Pinterest starts growing and becomes more of a destination for a greater audience. The more time users spend on Pinterest, one assumes, the less likely they are to click out to other sites. And why click out when you can see the whole picture right there?